U.S. Army Staff Sgt. Robert Bales, who is facing sentencing by a military court for killing 16 civilians on a rampage in Afghanistan last year, might have faced a perfect storm of stress, which included the use of mefloquine hydrochloride, an antimalarial drug given routinely to soldiers in that part of the world.

Mefloquine was developed by the U.S. military and has been used for more than three decades by the government to prevent and to treat malaria among soldiers and Peace Corps workers.

Sullivan said the military widely uses antimalarial drugs in Afghanistan, but mefloquine is not the first choice.

"Tens of millions of people take it," Sullivan said. "Honestly, you cannot implicate any one thing. To put it all on mefloquine is not fair. [Bales] already has a predisposition because of a traumatic brain injury and he has taken this drug in a stressful situation. You have to put it in context here. … But you can't exclude it."

Bales, 39 and the father of two from Washington state, has admitted to the killings after he left of his remote outpost in the southern Afghan province of Kandahar to go on a shooting spree in two nearby villages. The pre-dawn attack left 16 villagers dead and six injured. Nine of those killed were children.

There is "not a good reason in the world" for the "horrible things" he did, Bales testified in a military court in June.

Bales suffered from head and foot injuries while deployed in Iraq and might have been traumatized by seeing one of his fellow soldiers lose a leg in an explosion hours before the killings, according to testimony.

By pleading guilty, he avoided the death penalty, but Bales still faces life imprisonment, with or without parole, at a sentencing trial set for next month.

According to the adverse-event report from the pharmacist, a man of "unknown demographics" had a history of traumatic brain injury with "no other medications of past drugs. ... this patient was administered mefloquine in direct contradiction to U.S. military rules that mefloquine should not be given to soldiers who had suffered TBI (Traumatic brain injury) due to its propensity to cross blood brain barriers inciting psychotic, homicidal or suicidal behavior."

FDA spokesman Stephanie Yao said the report was "authentic." She said anyone could submit such a report, so it is impossible to know who wrote it.

"These are voluntary reports," she said. "They are anonymous mainly because of the regulations protecting patient information, so names are not included.

"Adverse-event reports are one of the tools we use to monitor the safety of a drug after it is approved," she said. "We encourage people, whether it's a patient or health professional or manufacturer, to submit, so when we see a trend we can look into it in the future to see if there is a safety issue.

"In clinical testing, we use smaller populations and once drugs are approved they are used in a much wider population and we must continue to monitor safety."

Bales' lawyer, John Henry Browne, told the Seattle Times last week that he has documents indicating his client took mefloquine while in Iraq, but Bales' medical records in Afghanistan were incomplete.

"He [Bales] can't help us," Browne said. "He just says he took 'whatever they gave me.'"

Browne did not return a call from ABCNews.com, and the Seattle Times reported that he did not indicate whether he would cite use of
mefloquine as a possible contributing factor to Bales' crimes at next month's sentencing.

According Time magazine, which first reported on the pharmacist's report, the initial summary eventually made its way to the FDA April 11.

Mefloquine, was first developed in the 1970s at the U.S. Department of Defense's Walter Reed Army Institute of Research as a synthetic analogue of quinine, the first effective treatment for malaria. It was licensed in 1989 by the FDA for use against chloroquine-resistant malaria.